linux-kernel - [PATCH v2 0/3] iommu/s390: Fixes related to repeat attach

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Message-Id: <20220922095239.2115309-1-schnelle@linux.ibm.com>
Date:   Thu, 22 Sep 2022 11:52:36 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>, iommu@...ts.linux.dev
Cc:     linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, joro@...tes.org, will@...nel.org,
        robin.murphy@....com, jgg@...dia.com, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/3] iommu/s390: Fixes related to repeat attach_dev calls 

Hi All,

This is a follow up to Matt's recent series[0] where he tackled a race that
turned out to be outside of the s390 IOMMU driver itself as well as duplicate
device attachments. After an internal discussion we came up with what I believe
is a cleaner fix. Instead of actively checking for duplicates we instead detach
from any previous domain on attach. From my cursory reading of the code this
seems to be what the Intel IOMMU driver is doing as well.

During development of this fix we realized that we can get rid of struct
s390_domain_device entirely if we instead thread the list through the attached
struct zpci_devs. This saves us from having to allocate during attach and gets
rid of one level of indirection during IOMMU operations. Coincidentally
I discovered that a previous list_head in struct zpci_dev is unused so this is
removed and then replaced.

The duplicate entry fix is the first patch of this series and the only one
which carries a Fixes tag. It may be applied alone or together with patches
2 and 3 which are followup clean ups.

Best regards,
Niklas

Changes since v1:
- After patch 3 we don't have to search in the devices list on detach as
  we alreadz have hold of the zpci_dev (Jason)
- Add a WARN_ON() if somehow ended up detaching a device from a domain that
  isn't the device's current domain.
- Removed the iteration and list delete from s390_domain_free() instead
  just WARN_ON() when we're freeing without having detached
- The last two points should help catching sequencing errors much more
  quickly in the future.

[0] https://lore.kernel.org/linux-iommu/20220831201236.77595-1-mjrosato@linux.ibm.com/

Niklas Schnelle (3):
  iommu/s390: Fix duplicate domain attachments
  s390/pci: remove unused bus_next field from struct zpci_dev
  iommu/s390: Get rid of s390_domain_device

 arch/s390/include/asm/pci.h |  2 +-
 drivers/iommu/s390-iommu.c  | 94 +++++++++++++++++--------------------
 2 files changed, 43 insertions(+), 53 deletions(-)

-- 
2.34.1